Recirculating ball heat transfer system for drying and heating materials

ABSTRACT

The helical screw(s) of a screw-type heat transfer device are efficiently cleaned by engaging the volute passages of a helical screw with recirculating balls which pass cooperatively along a longitudinal guide channel and at least partly within the volute passages of the helical screw to effect cleaning of the device.

United States Patent [191 Buttner Nov. 27, 1973 [76] Inventor: Horace J. Buttner, 117 W. 155th St., Gardena, Calif. 90427 [22] Filed: May 10, 1972 [21] Appl. No.: 252,080

Bearce 432/27 Gilbert 1. 165/ 1 07 Primary Examiner--Edward G. Favors Att0rney-William D. Hall et al.

[5 7 ABSTRACT U.S. The helical crew(s) of a screwq ype heat transfer de- 1 CI. i e are efficiently cleaned engaging the volute pas. Fleld of Search ages of a helical screw recirculating bans 165/107 pass cooperatively along a longitudinal guide channel and at least partly within the volute passages of the he References Cited lical screw to effect cleaning of the device.

UNITED STATES PATENTS 3,254,881 6/1966 Rusk 432/215 X 29 Claims, 12 Drawing Figures R',-MATER|AL OUTLET C F R \K v I M l l l s. K a 1 1 GI \f \l/ -S 6 MATERIAL INLET R PATENTEDRUVZY am 3775041 SHEET s BF 6 wirlfl 4 So 93m QZEGI QUE .mjv: EEWEE RECIRCULATING BALL HEAT TRANSFER SYSTEM FOR DRYING AND HEATING MATERIALS BACKGROUND OF THE INVENTION Various types of apparatus and methods are in use to evaporate volatile matter from fluent, wet or pasty materials. They are, for instance, dried by direct contact with hot gases. The treatment of large quantities of used drying gas to remove pollutants prior to their discharge into the atmosphere is a technical and economic problem. The need for such treatment could be reduced considerably if not eliminated through the use of screw-type heat exchangers which can transfer heat indirectly thus avoiding the need for large quantities of drying gases and after-treatment thereof. However, screw-type heat exchangers are subject to problem of clogging by materials of a thick consistency and suffer from the build-up of hard carbonaceous deposits on the screws which inhibit heat transfer and render such systems of limited usefulness. Reduction in temperatures can alleviate the rate of deposit; however, to reduce temperature while maintaining the desired through-put requires greatly increased heat transfer area at much greater cost. Since a constant scraping of surfaces is necessary to prevent this deposit build-up, intermittent or periodic removal is unfeasible.

It has been proposed to solve this problem by intermittently intermeshing the screw with scraping means. This requires complex mechanisms which require excessive maintenance. Other arrangements for continuously scraping inthe form of an interrneshing flexible tube or precision mating of an additional screw or screws result in binding and damage from deposits or unequal expansion of mating elements nullifying costly precise machining accuracy. Thus, the present invention has as its object'the provision of screw-type heat exchangers which run clean, thereby maintaining a high efficiency, and which are both durable and economical of construction.

SUMMARY OF INVENTION Simple and efficient apparatus and method for self cleaning screw-type heat transfer systems have been discovered. In accordance with the invention, means are provided for holding a plurality of balls in rollable or sliding contact with the screw in the heat transfer apparatus. Means are provided for heating the balls, directly and/or indirectly, such as through the screw or the walls of a channel or recirculation means referred to below, or by a combination of these or other means. Such a channel, which islocated in the housing of the apparatus, holds the balls so that at least a portion of their cross-section protrudes into the volute passage which exists between the flutes of the screw. Because the channel runs generally lengthwise of the housing along at least a portion of the screws length and is askew of (not in line with) the screw flutes, rotation of the screw positively urges the balls to move from an upstream end of the channel toward its downstream end. As a consequence there is a scrubbing action between the balls, and those surfaces of the screw and guide channel with which they come in contact. These surfaces are continually cleaned through the scrubbing action and the material is therefore continually being brought into contact with cleaned surfaces, thus improving heat transfer from the surfaces to the material.

The portions of the balls cross-sections which extend between the screw flutes continually displace wet or pasty material from between the flutes of the screw. This'increases the frequency of contact between the screw and different portions of the material which is under treatment. Also, contact between conductive heated balls and the fluent material provides additional heat transfer thereto, thus increasing the rate of heat transfer and the efficiency of the apparatus. Preferably, recirculating means are provided for transporting the balls from a downstream portion to an upstream portion of the channel so that they may be recirculated. Two or more screws and/or channels and sets of balls may be provided. The halls and channel(s) may be so arranged, if desired, to lend support to the screw(s), which provides a way of protecting such screw(s) against whipping or bending, permitting fabrication (l in longer lengths than previously possible with fewer or no intermediate supports and/or (2) with light-weight construction. Thus, reductions in weight, cost of materials and handling problems are realized. Invention is also believed to reside in other various details of the preferred apparatus and method which are described in the drawings and in the text which follows.

I BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a device for heating and/or drying according to the present invention, the housing being removed to reveal the interior, wherein there is used a single helical screw and multiple recirculating ball means.

FIG. 2 is a cross-sectional end view of FIG. 3 taken along line 2-2.

FIG. 3 is an internal side view of the subject matter of FIG. 2, wherein the housing and jacket of that figure have been removed along line 3-3.

FIG. 4 is an internal view of another embodiment of the present invention wherein the housing has been removed to reveal the interior of the device. This figure illustrates the use of a conventional mixing screw in conjunction with the recirculating ball heat transfer system of the present invention.

FIG. 5 is a detailed view of the relationship of a spherical ball to a helical screw and a channel.

FIG. 6 is a detailed cross-sectional view of the inlet end of a preferred embodiment of the present invention.

FIG. 7 is a detailed cross-sectional view of the outlet end of a preferred embodiment of the present invention.

FIG. 8 illustrates a construction of a scraping means which may be provided in the outlet end of the apparatus for scraping and cleaning the balls.

FIG. 9 is an internal view of an embodiment of the invention showing cam means for guiding the recirculating ball into the channel and out of the tubular recirculation passage and vice versa.

FIG. 10 is a cross-sectional view taken along lines 10- 10 of FIG. 9 showing the development of the cam means beyond the end flute at the discharge end of the device.

FIGS. 11A and 11B illustrate several types of volute passages of essentially semicircular cross-section within the meaning of the present invention.

DETAILED DESCRIPTION OF MAIN EMBODIMENTS OF THE INVENTION One embodiment of the invention, as represented by FIG. 1, comprises an elongated housing D having a material inlet, a material outlet, and including port means V for withdrawing gas and/or vapors from the housing. At least one elongated helical screw H is mounted on rotatable shaft S in the housing. The flutes F of screw I-I define a volute passage K which is preferably though not necessarily of substantially semi-circular crosssection.

In the housing is at least one elongated guide channel C extending in a straight or curved path along at least a portion of the length of the housing and the longitudinal axis of the screw. The channel is preferably though not necessarily of substantially semi-circular inner cross-section and of a radius essentially the same as the radius of the cross-section of the volute passage K. The channel has at least one open side (the other side being closed or partly open) facing toward the screw. The walls defining the channel C (as illustrated in the FIG. 2 embodiment) are spaced radially from the screw axis a suitable distance and have a suitable shape to maintain balls B in contact with the walls of volute passage K. The walls of the channel and passage may have varying configurations, for example V and U, which are effective to confine the balls against escape. It is however advantageous that walls which are intended to transfer heat be semi-circular; that is they are formed so that their surfaces, viewed in cross-section through the axis of the respective volute passage or guide channel, describe a semi-circle or portions thereof. This enables more thorough contacting and cleaning of the walls by the balls. Where both the channel C and passage K are of substantially semi-circular cross-section, the spacing of channel C from the screw axis is preferably such that its walls and those of the passage K contact substantially a complete circle about the peripheries of the balls B.

The channel is in its most simple and economical form, both straight and parallel to the screw axis. However, provided proper radial spacing is maintained, the

channel may follow a curved path which is askew of (not parallel with) the screw axis. Those skilled in the art will readily select proper angular relationships between the channel alignment and screw pitch to avoid unnecessarily large friction losses between the screw, balls, and channel as the screw turns.

The feeding means are formed and positioned upstream along channel C for bringing the balls into engagement with a pick-up portion of screw H with one or more components of motion in a plane which includes the screw axis and passes through the channel axis. There may also be a component perpendicular to this plane. Preferably, there is at least a component parallel to the screw axis, especially during initial contact of a ball with a screw, to help minimize the possibility of jamming. Indexing of each ball in sequence may be accomplished with a spring-biased cam surface or plunger forcing positive engagement of the ball with the lead-in volute.

If the upstream end of the screw has been cut away to provide a lead-in flute, the balls may be delivered to the screw while moving along the centerline or extended centerline of the channel, as shown in FIG. 6.

On the other hand, the feeding means may be positioned for bringing the balls into contact with the screw with components of motion both perpendicular and parallel to the screw axis in a direction towards the downstream end of the screw. When this is done with stationary guide means, such as a fixed cam surface attached to the housing at the pick-up point of the screw, this surface may be flat or curved, but converges towards the screw axis in the downstream direction. When the feeding cam means converge towards the screw at angles approaching 90, e.g., to 88 and more preferably about 83, this substantially reduces jamming problems attendant to location of the pick-up point of channel C intermediate the ends of the screw.

When the feeding means is provided as a stationary guide means, it is preferably to so construct the system that the balls entering the channel C are subjected to a force which urges them towards the screw. This positive force may be imparted, for example, by (l) the force of gravity, (2) the movement of balls being forced from the discharge end of the system to the inlet or feeding end of the system by way of a recirculating means (described below), (3) any suitable type of biasing means which will exert a positive pressure on the ball as it enters channel C, or (4) any combination of the above means. Other suitable means will become apparent to one of ordinary skill in the art and are within the scope of the present invention.

At a downstream position along the channel C are located means for removing balls from a pick-off portion R of the screw S. The removing means may take any desired form. In the preferred apparatus, the downstream end of the screw is cut away to provide a leadout flute and the balls may be removed from the screw while moving along the center line or extended center line of the channel, as shown in FIG. 7. However, the removing means may be arranged to separate the balls from engagement with the screw while imparting a radially outward component (relative to the screw axis) of motion thereto. As in the case of the feeding means, the removing means preferably includes a movable member, such as a spring, piston, plunger or the like. However, stationary removing means may also be used. This may, for instance, take the form of fixed cam surface G of any suitable shape attached to the housing at the pick-off point of the screw l-I. This surface may diverge from the screw axis (a) outwardly in the downstream direction; (b) in the direction of screw rotation when viewed perpendicular to the screw axis; and (c) in both directions (a) and (b). Also, the removing means may be located on the screw itself. Here again, any of various movable or stationary means may be employed, but the preferred means is a cam surface fixedly secured in the bottom of the volute passage at the screw pickoff position. This cam surface diverges from the screw axis (a) outwardly in the downstream direction; (b) in a direction opposite to rotation of the screw when viewed perpendicular to its axis; and (c) both (a) and (b). It is preferred that the cam surface extend radially such that the ball clears the next or following ball to enter the cam surface. As in the pick-up end of the screw it may be desirable to provide a springbiased cam surface, or plunger, to act as a detent, preventing return of a ball to the cam section of the screw.

In a preferred embodiment of the invention, recirculating means are provided to return balls from pick-off portion R to pick-up portion R, so that the balls may be continuously recycled through the channel C as screw H rotates. The recirculating means may take any suitable form, including such moving means as a screw or other conveyor. More preferably, however, a stationary passage P is employed. This passage may be defined by wire orrod ball guides, or confining walls of various cross-section, but preferably in the form of a closed tube having a diameter slightly larger than that of the balls B. In the most preferred form of the invention, the channel C and tubular passage P form or communicate through a U-shaped connection between their respective ends, such as is shown in FIGS. 1, 3, 4, 6 and 7. Also, it should be noted that as shown in the aforementioned figures, the feeding and removing means on the one hand and the aforesaid U-shaped connection on the other hand may be or include common elements of the apparatus. However, with appropriate feeding and removing means, the recirculating tube P and channel C may join with one another in other configurations, such as are shown in FIG. 9. In any event, the channel C, screw H, passage P and such portions of the feeding and removing means as may be included therein, preferably form an enclosed recirculating path for the balls B.

Balls B are spherical and of sufficient hardness and durability so that they may be recirculated limitless numbers of times through the apparatus while retaining their original dimensions sufficiently to be capable of continued use in the device. Included within this definition are metal balls (which are preferred), refractories, and highly brosslinked and/or highly abrasion resistant plastics. Preferably, the number of balls is chosen so as to substantially completely fill the recirculating path. This is not essential however, so long as the recirculating path is configured in a way which avoids jamming build-ups of balls in the vicinity of the removing means and shortages of balls at the heating means. This may be accomplished, for instance, by arranging the recirculating passage P so that there is gravity feed of balls from the vicinity of the removing means to the feeding means. Similarly, the feeding of the balls need not be conductedlin such a manner that every flute of the screw contains a ball, but operation with all flutes filled is definitely preferred, especially where the balls are being relied upon to support the screw. When the entire recircuilating path is filled with balls, the apparatus may then operate in a mode wherein the discharge of a ball into the recirculating passage P by removing means G urges the next ball through feeding means G into the pick-up portion R of the screw.

It is an advantage of the present invention that it provides considerable flexibility in the manner of supplying heat td the apparatus. For instance, heat may be supplied through the screw, if it is hollow, through the walls of the housing, through the walls of the channel C or recirculating passage P, or may be supplied directly to the balls themselves (such as through openings in the walls of recirculating passage P) or by any combination of these and other means.

Heat may be supplied to a hollow screw by passing steam or other heated fluids through the hollow space in a direction either countercurrent or cocurrent with the direction of the flow of the material to be dried. A fuel burner may also be provided in the interior of the screw.

If the balls are heated directly, this may be done by playing the flame from a burner directly upon them.

Where the balls are heated through the walls of the channel C or recirculation passage P, the channel and- /or passage may be provided with a jacket through which may be circulated steam, hot fluids or hot combustion gases.

Through the present invention, heat transfer in a screw type heat exchange device can be simplified in terms of the cost of construction and ease of operation of the device. For example, with one or more set of balls which are heated directly or indirectly at some point along their recirculating path(s), heating of the screw can be dispensed with. When multiple sets of balls are used, the heat transfer area can be made equal to that available from the use of a hollow heated screw of equivalent size to the nonheated screw used in the improved apparatus. In such a system, the costly, difficult to maintain, high temperature fluid transfer glands for the rotating hollow screws are eliminated.

On the other hand, if an internally heated screw is used, together with one or more sets of balls which are heated directly or indirectly along their recirculating path(s) by their own heating means, a 50 percent or greater increase in heat transfer area can be obtained, as compared with the heat transfer area available from the screw alone.

The continuous scrubbing of the spherical balls on the clean surfaces of the volute passage of the helical screw, the guide channel and the recirculating passage, assist in the transfer of heat between such surfaces and the balls. This scrubbing action also removes deposits which have formed and prevents the deterioration of heat transfer within the system by preventing any significant deposition of carbonaceous or other heat transfer resistant deposits on the scrubbed surfaces. Since such deposits increase in an amount that may double in rate with each small (i.e., 10F.) increment of temperature above 450F., conventional screw type heat transfer devices rapidly lose their heat transfer capabilities as a result of these deposits. With the scrubbing action of the balls preventing the build-up of deposits, the devices of the present invention are much less subject to temperature limitations than those previously employed.

Although the present invention has the advantage of providing clean running single screw heat transfer devices, additional screws may be provided for any worthwhile purpose. For instance, the second screw having its flutes extending between the flutes of the first screw, can assist in the mixing action. One or both of the screws may be provided with a recirculating ball system. The second screw may be driven by a common or independent drive system without contacting the main screw, and rotating in the same or opposite direction, or it may be driven by contact between the screws, thereby assisting in the cleaning action. One of the screws can be of the conventional type wherein the helical flutes and volute passage are formed by multiple ribbons of flat steel spirally wound about a shaft. One or both of the screws may be cast in a single piece. Or, one or both screws may be fabricated by spirally winding longitudinally split tube halves around a tubular or solid shaft with the curved surfaces of the tube halves being secured to the outer surface of the shaft (e.g., as by welding) as shown in FIG. 7. The tube halves may be wound on the shaft so that their edges are spaced apart, or so that the edges of adjacent turns are contiguous, in which case the contiguous edges may also be secured to one another, as by welding. The second screw does not necessarily have to have the outer edges (flutes) of its helical flutes intermeshing or overlapping with the flutes of the other screw and the screws may actually be spaced apart, if so desired, without departing from the scope of the invention. The preferred arrangement, however, is to provide two or more screws having intermeshing flutes and volute passages of semicircular cross-section. Such an embodiment is disclosed in detail in FIGS. 2 and 3.

In FIGS. 2 and 3, the flutes of each screw extend into the volute passages of the other screw, without touching same. This embodiment includes a heating jacket J surrounding housing D, channel C and recirculating passage P. Heat is supplied by a burner positioned at an opening in heating jacket J. Alternatively, instead of being opened at points A to allow passage of the gases through the jacket, the jacket may be totally closed off and thus completely enclose the heat transfer surfaces. Such complete enclosure is illustrated by the dotted lines at points A in FIG. 2. Where the jacket J so encloses the heat transfer drying system of the present invention, a heating medium such as steam may be introduced into the jacket J at any suitable point, recirculating through the jacket to heat the system.

Referring to FIG. 4, this Figure illustrates an embodiment of the invention wherein the helical screw H for conveying the material through the heat transfer drying system of the present invention, with its volute passages of essentially semi-circular cross-section K is combined with a conventional helical mixing screw M. The overlapping of the two screws is essentially the same as that shown and described with regard to FIG. 3. It should be noted at this point that the helical mixing screw M may be driven in a co-rotational or counter-rotational direction by a separate rotating means, not shown, or it may be driven by the rotating motion of the helical screw H.

Also in FIG. 4, it can be seen that there is an essentially U-shaped connection between the recirculating tubular passage P and the channel C within the housing D. There is also generally shown a guide means G for facilitating the smooth entry of the balls B from the tubular passage P into the channel C at the inlet end of the system and guide means G for the removal of the balls B from the channel C at the discharge end of the system, which guide means also serve to function as part of the U-shaped connection.

FIG. 4 also illustrates a different positioning for the vapor port or the gas withdrawal means V whereby the gases produced from the vaporization of the volatile components of the material to be dried are removed from the heat transfer drying system of the present invention. The position of this withdrawal port may be varied as desired to promote the efficient and proper operation of the recirculating ball heat transfer system of the present invention. If necessary, more than one such port may be provided within the housing to allow for the escape of the vapors produced within the system.

FIG. 5 illustrates more clearly the relationship between the balls B, the volute passages of essentially semicircular cross-section K and the channel C. The outer flutes edges E of the helical flutes F serve as the beginning and the end of the semicircle of the crosssection of the volute passages K. The ball B is of essentially the same radius as the radius of the semicircuoar cross-section of the volute passage K and fits snugly therein within the confines of the channel C of semicircular cross-section. The semicircular nature of the cross-section of the channel C is shown clearly at L of FIG. 2. The close relationship of the ball B to the volute surfaces as confined therein by the channel C is what effects the cleaning of deposits from the helical screw H according to the teachings of the present invention.

FIGS. 6 and 7 illustrate a preferred embodiment of the system of the present invention. FIG. 6 is the inlet end of a preferred embodiment of the present invention while FIG. 7 depicts the outlet end of a preferred embodiment. The housing is generally designated by D. The tubular recirculating passage is generally designated by P and the longitudinally extending ball guide channel provided in the housing is generally designated by C.

The helical screw shown in these figures is a hollow helical screw designated by 10. The screw is mounted on a hollow pipe shaft S so as to form a hollow helical passage designated by 5 through which a heating fluid (i.e., steam) may pass. The shaft S is mounted for rotation within the housing D and is engaged therewith on each end of the shaft S by way of bearings Seals are properly positioned around the bearings and shaft to prevent the escape of lubricating fluids from the bearing area and entrance of contaminants into the bearings from the process material or the atmosphere.

A stationary tube 7 extends a short distance into the shaft S. The stationary tube 7 communicates with tube 8 positioned within the interior of the shaft S and rotating with it. A piston ring seal gland 9 provides a lowleakage seal at the point of communication between tubes 7 and 8. At the exit or discharge end of the system, rotating tube 8 communicates with the helical path 5 by way of a fixed communication channel 4. Heating fluid is supplied from any suitable external fluid source into the stationary tube 7 and flows along the rotating tube 8 within the shaft S to the communication channel 4 and from there the heating fluid passes into the helical channel 5 so as to heat the surfaces of the helical screw 10. Spent heating fluid passes from helical path 5 through port 6 in shaft S to a passage between said shaft and the exterior of tube 8. An extension of this passage conveys the fluid through the bearing assembly to the heating fluid outlet. Thus, means are provided for circulation of the heating fluid and for its return to an external source (not shown).

At the discharge end of the system, the shaft S is connected to a drive shaft by way of a tension bolt T. It is this solid main shaft that is attached to a gearing or rotating means, which means is not shown in the figures.

As an additional source of heat for drying the material introduced into this system there is provided around the tubular recirculating passages P a heating jacket J. A heating fluid is introduced into the space between the jacket J and the tubular passage P which space is designated by the numeral 2. This fluid may be from the same external source or a different source from that of the heating fluid supplied to the stationary tube 7.

At the inlet end of the system, the connection between the tubular recirculating passage P and the channel C, through which the spherical balls 12 are transferred from the tubular passage P into the channel C, is effected by providing a U-shaped guide means 13.

This guide means 13 is pivoted about a point 14 so as to allow the guide means to introduce the balls 12 into axial engagement with the volute passage K as it appears under the channel C. The guide means thus pivoted at point 14- will allow for the intermittent action at both ends of the helical screw and the variation in the stack up and the wear of the balls during the course of operation of the system. A stop 15 in conjunction with a spring 16 cooperate with the guides 13 at the inlet end of the system so as to bias the balls 12 against the screw as they enter the volute passages K appearing under the channel C and yet still allow for the intermittent play and the wear of the system.

To allow for the expansion of the vapors as the volatile materials are vaporized in the heat transfer drying system shown in FIGS. 6 and 7, there is provided towards the discharge end of the system a vent space designated by 1. In FIG. 7 this vent space is shown as an enlargement of the channel C so as to provide a space between the surface of the balls and the inner surface of the channel. To prevent the loss of the solid materials entrained in the vapors as they are formed in the system, this vent space 1 can be connected, not shown, with the material inlet so that the vapors containing the entrained material are carried back into the inlet of the system, thus preventing the loss of any entrained solid materials. It should be noted that this vent space can be provided as a relatively large uniform space around the helical screw. The only limitation on the size of the vent space, excluding the channel C, is

that the housing immediately surrounding the inlet end of the helical screw into which the material to be dried is charged is in close proximity to the periphery of the flutes of the helical screw. This close proximity at the inlet end is needed so that a positive forward motion can be imparted to the material in order to convey the charged material towards the discharged end of the system. The vent space provided in channel C obviously cannot be so large as to allow for jamming of the balls. The semi-circular inner cross-section of the channel C should be maintained in relative close proximity to the balls 12.

As the balls 12 are carried from the inlet end of the system to the outlet end of the system by the rotational movement of the helical screw, they must be transferred from the channel C at the outlet or discharge end of the system into the tubular recirculating passage P at the discharge end of the system. This is effected through the use of a U-shaped guide means 17, which guide means 17 is fixedly connected to the housing D at point 18. The guide means extends to the base of the respective end flutes of the helical screw, as in the case with guide means 13. As with the guide means 13 at the inlet end of the system, the guide means 17 at the outlet end of the system terminate immediately adjacent the respective end flutes of the helical screw. Also, as do the guide means 13 at the inlet end of the system, the U-shaped guide means at the outlet end of the system serve to translate the axial motion of the balls, imparted to same by the helical screw, into a gradual change of direction of the balls from the channel C into the tubular recirculating passage P.

Situated at the discharge or outlet end of the system and cooperating with guide means 17 there are provided ball-cleaning means 19. As depicted in FIG. 7, these ball cleaning means comprise a number of scraping blades 20, which blades rotate preferably at a rate lower than the velocity of the balls so as to scrape any solid deposits off of the balls prior to their reentry into channel C at the inlet end.

FIG. 8 is a more detailed showing of the preferred method by which the balls are cleaned prior to their entry into the tubular recirculating passage. The ballcleaning means 19 comprises scraping blades 20 mounted on a shaft 21. The scraping blades are so formed as to have a semicircular scraping edge 22 which conforms to the spherical shape of the ball 12.

As can be seen from FIGS. 1, 3 and 4, the guide means designated generally by the letter G and G does not of necessity have to be one and the same with the U-shaped connection of the tubular recirculating passage P and the channel C as shown in the preferred embodiment of FIGS. 6 and 7.

FIGS. 9 and 10 illustrate an embodiment of the invention which employs a recirulation path only partially filled with balls, which extends along only a portion of the length of the screw, the channel and screw both being provided with cam or guide means. FIGS. 9 and 10 also illustrate a preferred cam means 50 which will effectively remove the balls from the channel C. In FIG. 9, the feeding cam means G located at the pick-up position of the screw is, when viewed in longitudinal cross section, at an angle a of 83 to the axis of the screw. As balls B move into contact with cam means G by gravity feed from recirculating passage P, the balls are urged from right to left as they move into contact with the rotating screw. As the balls are moved downstream in channel C by the flutes F, they eventually contact a cam means 50 formed as an integral part of the screw S at the downstream end of volute channel K. Cam means 50 smoothly elevates the balls, one by one, into the circular cross-section recirculation passage P. In the device of this embodiment, the housing G is conveniently constructed in two halves (only one of which is shown in FIG. 9). Each housing half may be essentially a mirror image of the other half and may contain half, respectively, of the channel C and recirculating passage P. This form of construction makes it convenient to employ either one of two channels at diametrically opposed sides of the screw S. Where it is desired to have three or four channels and sets of balls, the housing D may be fabricated in four quarters, each of which includes the respective halves of the various channels and recirculating passages. P.

FIG. 10 is a sectional view giving a more complete understanding of the development of the cam means 50. As indicated in phantom outline in FIG. 10, a cam extension 52, having outline 51 may be positioned in a plane normal to the screw axis for assisting in forcing the balls B further into the recirculation passage P. Where such cam extension extends outside the outer diameter of the flutes of screw 50, it may be necessary to form a corresponding annular clearnace passage in housing D.

FIGS. 12A and 12B illustrate volute passages of the helical screw which are not exactly semi-circular in crosssection but are within the scope of the present invention. These are only a few examples of many possible configurations for the volute passages. FIG. 12A illustrates an essentially semi-circular volute passage provided with a number of cut-out depressions X in the essentially semi-circular outline. Three such depressions are shown but clearly one or two would also be suitable. FIG. 12B illustrates an essentially semicircular volute passage K wherein the tips T of the helical flutes F have been removed. Thus it can be seen that the language essentially semi-circular" clearly contemplates volute passage of a cross-section that is not exactly semi-circular in nature.

When more than one helical screw is incorporated in a device constructed in accordance with the invention, it is preferred that the screws cooperate in conveying the material from the inlet to the outlet of the system. The two screws can be co-rotating or counter-rotating. lf counter-rotating, it is necessary that the screws be oppositely spiralled. If co-rotating, it is preferred that they both be spiralled in the same direction. Where the co-rotating screws interrnesh, it is necessary that they be spiralled in the same direction to provide the desired additional mixing action.

It will be apparent to those skilled in the art that many variations can be made which are not specifically disclosed above, but which do fall within the scope of the invention. Accordingly, it is intended to protect all embodiments of the invention which fall within the scope of the claims below.

Having thus described my invention, I claim:

1. In a method of heat treating a fluent material wherein said material is heated and caused to move through a housing in engagement with a rotating screw having a volute passage formed therein, the improvement which comprises maintaining a plurality of balls in rolling or sliding contact with said screw and said material as said screw rotates; moving said balls downstream in said housing in response to rotation of said screw; and recirculating said balls from a downstream pick-off portion to an upstream pick-up portion of said screw, whereby said balls are continuously recirculated in contact with said screw for preventing and removing deposits on said screw.

2. The process of claim 1 wherein heat is supplied to said material through said screw.

3. The process of claim 1 wherein heat is supplied to said material through said balls.

4. The process of claim 1 wherein heat is supplied to said material through both said screw and said balls.

5. The process of claim 1 wherein said screw is heated by direct impingement of burning combustion gases thereon.

6. The process of claim 1 wherein said screw is internally heated by direct impingement of burning combustion gases thereon.

7. The process of claim 1 wherein said balls are heated by the direct impingement of burning combustion gases thereon.

8. The process of claim 1 wherein said balls are heated indirectly through the surfaces they contact.

9. The process of claim 1 wherein said balls are cleaned during each recirculation thereof, while out of contact with said screw.

10. The process of claim 1 wherein said balls are brought into contact with said screw with a component of motion parallel to the screw axis.

1 1. In a heating apparatus of the type having a housing in which is mounted a rotatable screw, said screw having flutes that define a volute passage therebetween, the improvement which comprises: channel means in said housing alongside said screw for maintaining a plurality of balls in contact with said screw and for guiding them downstream in said housing upon rotation of said screw; and means for recirculating said balls from a pick-off position along said screw to an upstream pick-up position, whereby said balls continuously clean at least a portion of said screw on rotation thereof.

12. A self-cleaning screw-type drying device for fluent, wet or pasty materials, which device comprises:

A. an elongated housing having a material inlet, a

material outlet, and including means for withdrawing vapor from said housing;

B. at least one elongated helical screw mounted on a shaft within said housing, said helical screw including volute passages between the flutes of said screw;

C. means for heating said material in said housing;

D. said housing including at least one channel, ex-

tending along at least a portion of the length of said housing and spaced radially from the longitudinal axis of said screw;

E. guide means located at the respective ends of said channel to facilitate the transport of spherical balls from one end of said channel and reentry of said balls into the other end of said channel;

F. recirculating means communicating with said channel at each end thereof and including a U- shaped connection between the respective ends of said channel and the corresponding ends of a recirculating passage, said recirculating means and said channel forming a recirculating path for a plurality of balls; and

G. spherical balls at least partially filling said recirculation path and contacting the walls of said volute passage and said channel.

13. The apparatus of claim 12 wherein said housing contains therein two or more of said elongated helical screws each mounted on a shaft; wherein means are provided for rotating said helical screws in the same or opposite directions; and wherein the outer flutes of each screw overlap those of the other screw.

14. The apparatus of claim 12 wherein said housing contains an elongated helical screw having volute passages of essentially semicircular cross-section.

15. The apparatus of claim 12 wherein said housing is provided with two or more of said channels adjacent at least one of said helical screws.

16. The apparatus of claim 12 wherein said housing is provided with two or more of said channels adjacent each of said helical screws.

17. The apparatus of claim 13 wherein said channels are straight and parallel to a screw axis and are spaced apart distances from one another around the periphery of said housing surrounding said helical screw.

18. The apparatus of claim 12 wherein said guide means located at the respective ends of said channel in said housing comprise cam means, positioned to smoothly direct passage of said balls from said channel into said recirculating passage and from said passage into said channel so as to avoid jamming or blocking of said balls in said apparatus.

19. The apparatus of claim 12 wherein said guide means is a scoop which serves to translate the axial motion of said ball imparted by said screw into a gradual change of direction of said ball from said channel into said tubular passage.

20. The apparatus of claim 12 wherein there is provided, (l) at the end of said channel wherein said balls reenter said channel from said tubular passage and (2) as an integral part of said guide means, a means for automatically biasing said balls into the first of said volute passages underlying said end of said channel and adjusting automatically for variation in stack up of said balls in said tubular passage and also for wear of said balls and said helical screw.

21. The apparatus of claim 12 wherein there is provided a means for cleaning said balls along said recirculation path.

22. The apparatus of claim 12 wherein said helical screw is hollow, wherein said shaft is hollow, and wherein said heating means include stationary or rotating burner means positioned within said hollow shaft.

23. The apparatus of claim 12 wherein said heating means includes means for the direct heating of 1) said housing, (2) said channel, or (3) said tubular passage containing said balls, or any combination of (l), (2) and (3).

24. The apparatus of claim 12 wherein said heating means includes a jacket surrounding (1) said housing with said channel, (2) said tubular passage containing said balls, or both (1) and (2), and wherein steam or hot fluid injection means are provided in said jacket so as to provide for the circulation of high temperature steam or hot fluid within said jacket.

25. The apparatus of claim 12 wherein said jacket is spaced from (1) said housing with said channels, (2) said tubular passage containing said balls, or both (1) and (2) a distance of from about 0.015 to about 0.025 inches.

26. The apparatus of claim 12 wherein said jacket is spaced apart from (1) said housing with said channels, (2) said tubular passage containing said balls, or both (1) and (2) a distance sufficient to provide a heating fluid velocity of at least about 5 feet per second.

27. The apparatus of claim 12 wherein said housing includes a vent space around said screw for gases to expand into, but wherein the housing immediately surrounding the inlet end of said helical screw into which said material to be dried is charged is in close proximity to the periphery of the flutes of said helical screw.

28. The apparatus of claim 12 wherein said means for withdrawing gas from said housing communicates with said material inlet so that any entrained solids carried off with the vapor formed during drying are recirculated rather than emitted into the air or otherwise lost.

29. The apparatus of claim 12 wherein said helical screw is hollow, wherein said shaft is hollow, wherein the hollow space of said shaft and the hollow space of said screw communicate at at least one point, wherein means are provided for introducing and circulating heating fluid into said shaft and through said communication into and through said hollow screw, said heating fluid flowing in a direction opposite to the direction of flow of said material or in the same direction as the direction of flow of said material, and wherein means are provided for venting off the heating fluid after it has been so circulated returning said fluid to an external source.

' UNID STATES PATENT IOVFFIICE W69) @ERTI'FICATE OF CURB FICTION p ,775, 041 Dated November 27,- 1 973 HORACE J. BUTTNER Inventor(s) It is certified that error appears in the above-identified patent "and that said Letters "Patent are hereby corrected as shown below:

. a) On the cover sheet .in item [76] delete 117 W. 115th $11., Gardena, Calif. 90427" and insert 1501 Palos Verdes Drive, North, Harbor City, California 90710 b) In item 7 56] insert the following references made of record by the Examiner:

' 1,795,348 3/1931 Schmidt 165/95 3,255,814 6/1966 Zimmerman et a1 165/87 3,367,201 2/1968 Orner 74/424.8 3,369,422- 2/1968 Sears 74/424.8 3,369,598 2/1968 List 165/90 7 3,399,581 9/1968 Valenti et a1 i 74/424.8 3,457, 9 89 7/1969 Nonnemnacher et al 165/87;

c) And in the figure on the cover sheet, delete the lowermost "5'' and insert --H--.

d) In FIG.1, delete the lowermost "S" and insert -H-.--.

e) In column 2, line 35, insert --lof FIG.3- before the period.

f) In column 2, line 38, insert of FIG.'2'- before the period. Y

g) In column 4, line 6, insert --G-- after "surface". I

h) In column 6, line .29, delete "assist" and insert assistsi) In column 7, line 3, delete "(flutes)" and insert L j) 0' line 4, delete "flutes" and insert J Page 1 0f 2 ro-woso UNITED STATESIPATENT OFFICE.

569 CERTIFICATE OF CORRECTION Patent No. Dated November 27, 1973 Inventor) UT'INER It is certified that error appearsiri the above-identified patent and that said Letters Patent are hereby corrected as shown below:

outer edges ofthe flutes F k) v line 64 delete "flutes" and" insert --flute--;

l) Y O line 67 delete "semicircuoar" and insert semicircul'ar-. m) In colun mr8, line 23, insert a period after "bearings" n) In column 9, line 7, delete "cooperate'Fand insert cooperates 0) In column 10, line 50, delete "51" and insert 51' I line 54, delete "50" and insert --'H-- g) line 55, delete "'clearnace" and insert clearanoe--; 1

'r)- line 57, delete "12A and 12B"- and insert 11A and llB--;

s) Q line 61, delete "12A" and insert --llA-;

t) g line 66, delete 12B and insert llB- and u) In columnl2, line 47, delete "l3" and insert --l2--.

Signed and sealed this 29th dayof October 1974.

(SEAL) Attest: v McCOY M. GIBSON JR. 0. MARSHALL DANN n Attesting Officer Y Commissioner of Patents 

1. In a method of heat treating a fluent material wherein said material is heated and caused to move through a housing in engagement with a rotating screw having a volute passage formed therein, the improvement which comprises maintaining a plurality of balls in rolling or sliding contact with said screw and said material as said screw rotates; moving said balls downstream in said housing in response to rotation of said screw; and recirculating said balls from a downstream pick-off portion to an upstream pick-up portion of said screw, whereby said balls are continuously recirculated in contact with said screw for preventing and removing deposits on said screw.
 2. The process of claim 1 wherein heat is supplied to said material through said screw.
 3. The process of claim 1 wherein heat is supplied to said material through said balls.
 4. The process of claim 1 wherein heat is supplied to said material through both said screw and said balls.
 5. The process of claim 1 wherein said screw is heated by direct impingement of burning combustion gases thereon.
 6. The process of claim 1 wherein said screw is internally heated by direct impingement of burning combustion gases thereon.
 7. The process of claim 1 wherein said balls are heated by the direct impingement of burning combustion gases thereon.
 8. The process of claim 1 wherein said balls are heated indirectly through the surfaces they contact.
 9. The process of claim 1 wherein said balls are cleaned during each recirculation thereof, while out of contact with said screw.
 10. The process of claim 1 wherein said balls are brought into contact with said screw with a component of motion parallel to the screw axis.
 11. In a heating apparatus of the type having a housing in which is mounted a rotatable screw, said screw having flutes that define a volute passage therebetween, the improvement which comprises: channel means in said housing alongside said screw for maintaining a plurality of balls in contact with said screw and for guiding them downstream in said housing upon rotation of said screw; and means for recirculating said balls from a pick-off position along said screw to an upstream pick-up position, whereby said balls continuously clean at least a portion of said screw on rotation thereof.
 12. A self-cleaning screw-type drying device for fluent, wet or pasty materials, which device comprises: A. an elongated housing having a material inlet, a material outlet, and including means for withdrawing vapor from said housing; B. at least one elongated helical screw mounted on a shaft within said housing, said helical screw including volute passages between the flutes of said screw; C. means for heating said material in said housing; D. said housing including at least one channel, extending along at least a portion of the length of said housing and spaced radially from the longitudinal axis of said screw; E. guide means located at the respective ends of said channEl to facilitate the transport of spherical balls from one end of said channel and reentry of said balls into the other end of said channel; F. recirculating means communicating with said channel at each end thereof and including a U-shaped connection between the respective ends of said channel and the corresponding ends of a recirculating passage, said recirculating means and said channel forming a recirculating path for a plurality of balls; and G. spherical balls at least partially filling said recirculation path and contacting the walls of said volute passage and said channel.
 13. The apparatus of claim 12 wherein said housing contains therein two or more of said elongated helical screws each mounted on a shaft; wherein means are provided for rotating said helical screws in the same or opposite directions; and wherein the outer flutes of each screw overlap those of the other screw.
 14. The apparatus of claim 12 wherein said housing contains an elongated helical screw having volute passages of essentially semicircular cross-section.
 15. The apparatus of claim 12 wherein said housing is provided with two or more of said channels adjacent at least one of said helical screws.
 16. The apparatus of claim 12 wherein said housing is provided with two or more of said channels adjacent each of said helical screws.
 17. The apparatus of claim 13 wherein said channels are straight and parallel to a screw axis and are spaced apart distances from one another around the periphery of said housing surrounding said helical screw.
 18. The apparatus of claim 12 wherein said guide means located at the respective ends of said channel in said housing comprise cam means, positioned to smoothly direct passage of said balls from said channel into said recirculating passage and from said passage into said channel so as to avoid jamming or blocking of said balls in said apparatus.
 19. The apparatus of claim 12 wherein said guide means is a scoop which serves to translate the axial motion of said ball imparted by said screw into a gradual change of direction of said ball from said channel into said tubular passage.
 20. The apparatus of claim 12 wherein there is provided, (1) at the end of said channel wherein said balls reenter said channel from said tubular passage and (2) as an integral part of said guide means, a means for automatically biasing said balls into the first of said volute passages underlying said end of said channel and adjusting automatically for variation in stack up of said balls in said tubular passage and also for wear of said balls and said helical screw.
 21. The apparatus of claim 12 wherein there is provided a means for cleaning said balls along said recirculation path.
 22. The apparatus of claim 12 wherein said helical screw is hollow, wherein said shaft is hollow, and wherein said heating means include stationary or rotating burner means positioned within said hollow shaft.
 23. The apparatus of claim 12 wherein said heating means includes means for the direct heating of (1) said housing, (2) said channel, or (3) said tubular passage containing said balls, or any combination of (1), (2) and (3).
 24. The apparatus of claim 12 wherein said heating means includes a jacket surrounding (1) said housing with said channel, (2) said tubular passage containing said balls, or both (1) and (2), and wherein steam or hot fluid injection means are provided in said jacket so as to provide for the circulation of high temperature steam or hot fluid within said jacket.
 25. The apparatus of claim 12 wherein said jacket is spaced from (1) said housing with said channels, (2) said tubular passage containing said balls, or both (1) and (2) a distance of from about 0.015 to about 0.025 inches.
 26. The apparatus of claim 12 wherein said jacket is spaced apart from (1) said housing with said channels, (2) said tUbular passage containing said balls, or both (1) and (2) a distance sufficient to provide a heating fluid velocity of at least about 5 feet per second.
 27. The apparatus of claim 12 wherein said housing includes a vent space around said screw for gases to expand into, but wherein the housing immediately surrounding the inlet end of said helical screw into which said material to be dried is charged is in close proximity to the periphery of the flutes of said helical screw.
 28. The apparatus of claim 12 wherein said means for withdrawing gas from said housing communicates with said material inlet so that any entrained solids carried off with the vapor formed during drying are recirculated rather than emitted into the air or otherwise lost.
 29. The apparatus of claim 12 wherein said helical screw is hollow, wherein said shaft is hollow, wherein the hollow space of said shaft and the hollow space of said screw communicate at at least one point, wherein means are provided for introducing and circulating heating fluid into said shaft and through said communication into and through said hollow screw, said heating fluid flowing in a direction opposite to the direction of flow of said material or in the same direction as the direction of flow of said material, and wherein means are provided for venting off the heating fluid after it has been so circulated returning said fluid to an external source. 